Chloral Hydrate in Canadian Drinking Water

摘要

Chloral hydrate (CH) and aliphatic aldehydes are generally found at higher levels in drinkingwater that has been disinfected with ozone. In laboratory studies, CH was formed from thechlorination of acetaldehyde (ACD) at pH > 7 but not from methyl glyoxal. Controlledlaboratory studies on the chlorination of acetaldehyde under conditions of pH (6.7, 7.6, 8.8) andtemperatures (4°C and ca 21°C) typical of Canadian drinking water supplies revealed that thelevel of CH increased initially with contact time (0 to 10 days). However, at higher pH (8.8) andtemperature (21°C), CH reached maximum levels within 2 days and subsequently decreased witha concurrent increase in the level of chloroform (TCM), but < 50% of the available ACD wasconsumed after 10 days contact time and only 63% of the molar concentration of ACDconsumed appeared as CH or TCM. In a survey of 6 drinking water facilities, CH was observedin water samples at pH < 7 which indicates that the chlorination of ACD is not the only precursorof CH in Canadian drinking water supplies and the increased levels of CH in ozonated watercannot be explained solely from the chlorination of ACD. In the survey, a suite of aldehydes(including ACD) and CDBPs (including TCM and CH) were found in the treated and distributedwater from all three treatment processes. The levels of CH exceeded the WHO provisionalguideline of 10 μg/L in 7 of 60 individual samples, in 1 of 12 seasonal averages and 0 of 6 yearlyaverages.